A hydraulic brake booster, such as shown in U.S. Pat. application Ser. No. 885,825, includes a housing which supports a control valve and a piston and substantially defines a pressure chamber. An input assembly extends into the housing and cooperates with the control valve to communicate fluid pressure to the pressure chamber. The piston is movable relative to the housing in response to fluid pressure in the pressure chamber to effectuate a brake application.
The input assembly includes a rod extending into the housing and a lever engageable with the control valve and the piston. The rod is movable to pivot the lever about the piston in order to move the control valve to a position communicating fluid pressure to the pressure chamber. If the fluid pressure communicated to the pressure chamber is insufficient to move the piston, the rod or lever is movable relative to the piston to open communication between a storage chamber and the pressure chamber, thereby providing a safety brake application.
During a brake application, the input assembly is movable with the piston so that the ratio of the input movement to the output movement is substantially constant. As a result, the input assembly must travel substantially the same distance as the piston before hydraulic "slack" and brake shoe clearances are taken up.